Abstract:
For years, government scientists celebrated that blockbuster inventions built with tiny building blocks -- the offspring of nanotechnology -- were just around the corner. Now, they are ramping up efforts to make sure this ultra-small stuff is safe. They must, since new questions abound: Can particles tens of thousands of times more narrow than human hair penetrate human skin, lungs or brain?

"We don't want to say nanotechnology is bad. You cannot paint it with a single brush," said Nigel Walker, the lead toxicologist of the National Toxicology Program's nano-scale evaluation program. "But one has to accept that some of it probably will be bad."